SQL Server Books online defines the DTC wait stat type as “Occurs when a task is waiting on an event that is used to manage state transition. This state controls when the recovery of Microsoft Distributed Transaction Coordinator (MS DTC) transactions occurs after SQL Server receives notification that the MS DTC service has become unavailable.

This state also describes a task that is waiting when a commit of a MS DTC transaction is initiated by SQL Server and SQL Server is waiting for the MS DTC commit to finish.”